Amorphous and partially crystalline (generally referred to as semi-crystalline) polymers can provide elastomeric properties as defined, for example, in ASTM D1566. An important class of elastomers is derived from polyolefins, generally using addition polymerization with a Ziegler-Natta type catalyst system. Currently, polyolefin elastomers are interpolymers of ethylene, a crystallinity-disrupting α-olefin such as propylene, which provides short chain branches, and optionally small amounts of a polyene, such as a diene, to provide unsaturated short chain branches useful in providing crosslinks between different chains. These interpolymers may be ethylene propylene copolymers (EP) not containing units derived from diene, or ethylene propylene diene terpolymers (EPDM).
Different technologies exist for curing EP and EPDM interpolymers. Curing can proceed progressively from an initial creation of long chain branches where a macromer or polymer chain inserts itself along the length of an already formed polymer, to an intermediate form in which the cured polymer is partly soluble and partly insoluble, to a fully cured form in which the bulk of it is insoluble and substantially all polymer chains are linked into a network and no isolated polymer chains remain for individual extraction.
A person skilled in the art selects the interpolymer, the curing/crosslinking systems, and other formulation ingredients to balance processability and physical properties of the final product such as aging, hardness, extensability, compression set, tensile strength, and performance when cold.
EP 964641, EP 946640, EP 1003814, U.S. Pat. No. 6,245,856, and U.S. Pat. No. 6,525,157, and others disclose polyolefin interpolymers that are elastomers and have crystallinity resulting from isotactically-arranged propylene-derived sequences in the polymer chain. This is in contrast with the EP and EPDM interpolymers in current commercial use whose crystallinity is due to ethylene-derived sequences. The properties of such propylene-based elastomers are different in many aspects from known EP and EPDM interpolymer elastomers. Use of dienes for these new propylene-based elastomers has been contemplated. See, for example, WO 00/69964, including at page 15, lines 18 to 25.